The most expensive residential property ever sold in New York — a $53 million mansion snapped up by a private equity kingpin in 2006 — is up for sale again, The Wall Street Journal reported Saturday.

J. Christopher Flowers has been quietly marketing his East 75th Street townhouse near Fifth Avenue, said people familiar with the matter. He was asking for around $50 million, though brokers said buyer interest was more in the range of $40 million to $45 million.

In addition to his record purchase price for any residential sale in Manhattan, according to data from StreetEasy.com, Flowers spent at least another $4 million to gut the building and demolish the foundation, Propertyshark.com records showed.

Some people who know the property, however, said he spent more than that to prepare the townhouse for renovation — meaning Flowers would have a hard time avoiding a loss of millions of dollars on a sale of the property in the range currently sparking buyer interest.

Flowers has never lived in the 114-year-old mansion and was selling because he is separated from his wife, said people familiar with the matter.